The fat embolism syndrome (FES) in forensic practice is observed usually in cases of polytrauma related deaths. FES is rare, but serious complication after trauma. The most cases of post traumatic fat embolism are not fatal and it's very likely that many cases of mild fat embolism are overlooked. We describe a case of fat embolism syndrome in a young man after high energy injury. Upon concrete ceiling fell on his shoulders he had open fractures of both tibias and massive haematoma of the left hip joint. Transport immobilization of both legs was performed with admitting of analgesia during transportation to the hospital. Immediately after admission to hospital he underwent surgery. Several hours after osteosynthesis of both tibias, in ICU patient became hemodinamically and respiratory unstable. He developed global cyanosis and metabolic acidosis with significant decrease of oxygen pressure in the blood. Control chest radiograph showed typical "snow-storm" like pulmonary infiltrations. Deep bradicardy occurred followed by cardiopulmonary arrest. CPR was unsuccessful and the patient suddenly died within 12 hours from the incident. Histologic confirmation of fatty droplets the most commonly observed in the lung capillaries, brain capillaries or disseminated throughout the body remains diagnostic standard. We present one case of FES to emphasize the arising need of a quantitative analysis of both the size and localization of the fat emboli in order to grade the severity of FES and its relative contribution in pathophysiology of death. The postmortem diagnosis of fat embolism syndrome (FES), traditionally based on the histological demonstration of fat globules seems not to be enough, nowadays. A quantitative analysis of both the size and localization of the fat emboli has been discussed as reliable method of grading the pulmonary fat embolism in order to determine its relative functional contribution in death pathogenesis.